Method for the manufacture of high butyryl cellulose esters



Patented Dec. 16, 1952 METHOD FOR THE MANUFACTURE OF HIGH BUTYRYLCELLULOSE ESTERS George A. Richter, Ervin L. Perkins, and Lloyd E.Herdle, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester,N. Y., a corporation of New Jersey No Drawing. Application June 5, 1950,Serial No. 166,292

'7 Claims.

This invention relates to a process of making high butyryl celluloseesters in which cellulose fiber is activated by treatment with water,the water is replaced by a lower aliphatic alcohol, formic acid, aceticacid, a low molecular weight ester or ketone or acetonitrile, followedby replacement of the water-displacing liquid with butyric acid free ofcatalyst.

It is well known that cellulose is more readily susceptible to acylationif it is first pretreated or activated. Most of the pretreatmentprocesses heretofore have involved a preliminary soaking of thecellulose with acetic acid, either with or without catalyst. Of recentyears the value of aqueous acids for that purpose has been recognized.However, cellulose which has been treated with aqueous acid or water andwhich has a high moisture content is difiicult to properly esterify withacid anhydride due to the vigorous nature of the reaction which occurswhen water and acid anhydride are contacted in the presence of catalyst.The pretreatment of cellulose with water, followed by displacement ofthe water from the cellulose with acetic acid prior to its use in theesterification process has been suggested, but in the case of themanufacture of high butyryl cellulose esters the acetic acid whichordinarily has been employed for that purpose decreases the proportionof butyryl which can be introduced into the cellulose. If butyric acidis employed directly for the purpose of displacing the water in thecellulose, the time of esterification materially exceeds that necessaryfor the esterification of cellulose activated by our process.

One object of our invention is to provide a method for activatingcellulose in a rapid manner preparatory to butyrylation. Another objectof our invention is to provide a process for activating fibrouscellulose in sheet form in which the convenient sheet form is retainedthroughout the activation preparatory to butyrylation. A further objectof our invention is to provide a process for activating cellulosepreparatory to butyrylation in which the cellulose when ready foresterification is substan tially free of moisture. A still furtherobject of our invention is to provide a method of activating fibrouscellulose in sheet form whereby the cellulose is rendered more reactivefor the preparation of cellulose esters having a high butyryl contentthan is obtained with a single stage method. Other objects of ourinvention will appear herein. a

Our invention in its broadest aspects comprises applying moisture to afibrous cellulose sheet at a temperature of -100 C. whereby thecellulose is quickly and uniformly activated, followed by replacing thewater with one of the fol-', lowin displacing liquids: methanol,ethanoLacetone, formic acid, acetic acid, acetonitrile, methyl formateand methyl ethyl ketone, which procedure is followed by the replacementof the displacing liquid with butyric acid. This sheet which has thusbeeen activated is then employed in an esterification in which butyricanhydride is employed as an esterifying anhydride, thereby obtaining ahigh quality cellulose ester having a high butyryl content.

A convenient method for activating cellulose in accordance with ourinvention is to pass the cellulose in sheet form in a continuous mannerover a series of suction boxes by the procedure illustrated in ourPatent No. 2,484,455. In'the first part of the treatment the cellulosesheet has water at a temperature of 70-100 C. sucked therethrough for atime of at least 10-20 seconds. Any time greater than this will give thesame effect but ordinarily is unnecessary and cuts down the rapidity ofthe operation. After the cellulose has been thoroughly moistened in thisfashion and suction has been applied thereto, the sheet, with or withoutpassing through pressure rolls, is then subjected to a sucking throughof a displacing liquid, such as one of the liquids mentioned heretofore,this treatment being continued until the moisture is substantially alldisplaced from the cellulose. This treatment need only take 10 to 20seconds although here again a longer time may be used if for any reasonthe individual operator desires to use a longer period at this point.After the moisture has been displaced from the cellulose sheet, thecellulose, with or without treatment with pressure rolls, is thensubjected to treatment with butyric acid, such as by sucking the butyricacid through the sheet thereby removing the displacing liquid. Thebutyric acid employed contains little or no moisture and may be used asis, or in some cases it may be desirable to incorporate a smallproportion of catalyst therein, which operation distributes the catalystuniformly throughout the cellulose sheet.

After the treatment of the cellulose sheet in the manner described, itis preferably broken up and employed in an esterification in which Wehave found that the method of activation described herein in which thewater is displaced with a displacing liquid and this displacing liquidis then displaced with butyric acid that the time of esterification isappreciably lessened as (30.1 pared with an activation method in whichthe moisture is replaced directly by the butyric acid. In case a shortesterification period is maintained, quality of the first stage dope asobtained with the two-stage displacement sequence is appreciably betterthan when butyric" acid is used directly to remove water from the sheet.For instance, in comparative esterifications in. one case using thesequence of. water displacement with acetic acid, and then withbutyricacid, and in a second case the sequence of water and displacement withbutyric acid, the time of esterification was appreciably shortened inthe first case using butyric anhydride as the esterifying agent undersubstantially the same esterification conditions. The cellulose employedin accordance with our process may beeither cotton linters orv refinedwoodpulp. However, as the latter material. is ordinarily marketed insheet form, our method of activation is especiall adapted for woodpulppretreatment.

Some procedures where cellulose treated in accordance with our inventionis useful, are for instance processes in which pulp sheet afteractivation and while wet with one part of butyric acid (such as resultsafter pressing) is picked apart andthen charged to an est'erificatio-nmixer to which a butyrylating'mixture had been added, such as where thereaction mass having an initial temperature of 35-40-C. is of thefollowing composition:

Parts Cellulose (dry weight basis) 1 Butyric acid 1 Butyric anhydridenu;3 Acetic anhydride .7 Butyric acid .2 Sulfuric acid; .03

By controlling the temperature and agitating for a time of 4-6 hours, ahigh butyryl cellulose acetate butyrate is obtained. If only butyricacid and anhydride is employed, a cellulose butyrate is obtained. 7

The following examples illustrate our invention:

Example I One part of a sheet of acetylation grade refined wood pulp'was treated using a vacuumof 4 cm. of mercury under the sheet by pullingtherethrough. the following. liquids in the order and for the timesindicated:

100 parts distilled water at 80 C. seconds 30 25. parts of methanol at30 C. do 15 25 parts of butyric acidat 30 C do 7 100' parts of butyric'anhydride containing 0.3% sulfuric acid at -l C. seconds 70 Theunpressed sheet was then placed in an esterification vessel containing6.5 parts of acetic anhydride and 10.6 parts of butyric acid per 9 partsof cellulose at 0 C. Enough butyric anhydride was added to make thetotal anhydride 26 parts per 9 parts of cellulose. The reaction mass wasmechanically agitated while cooling until a viscous reaction product wasobtained. The mass was then diluted with 108 parts of 96.5% acetic acidper 9 parts of cellulose and was mechanically agitated whereupon thephysical characteristics thereof were determined as re- 4 gards haze,color and fiber. The haze was determined as 36, the fiber as 5, and thecolor as 130.

The haze reading is determined as the depth in centimeters through whicha standard stainless steel wire can be seen as. it is lowered. into thedope. Color is measured as p. p. m. of platinum as chloroplatinate bycomparison with color standards containing enough cobalt chloride togive the proper red content for color comparison with the celluloseester reaction mass. The fiber readings are in parts of unesterifiedfiber per million parts. of mass being examined.

Example II The procedure'of Example I was repeated except that formic.acid was employed as the liquid to displacethe water. The values of theresulting product were: haze, 28; color, 150; and fiber, 30.

Example III Example I was repeated except. that acetone was employedinstead of. methanol. The values obtained were: haze, 23.5; color, 150;and fiber, 15.

Example IV A sheet of acetylation grade refined cotton linters wasactivated by drawing through the sheet the following liquids in theorder listed, in one case the fatty acid being. acetic acid, and in asecond case, butyric acid:

100'parts of water at C. 50 parts of fatty acid at 80 C. 25parts butyricacid at30 C.

A sheet was then pressed between: stainless steel rolls so that itconsisted of equal parts of cellulose and acid. Eighteen partsof sheetcomposed of nine parts of cellulose and. nine parts of. butyric acidwere placed-in the followin mixture having atempera-ture of 38 0.:

Parts Butyric anhydride 26 Acetic anhydride 6.5 Butyric acid 1.5Sulfuric acid .27

The mixture was agitated while using surrounding baths thereon havingthe following temperatures:

38 C. bath for 15 minutes 10 C. bath for 20 minutes 30- C. bath for 3hours 35 C. bath for 1 hour Clarity Vis- (cmi) cosity Color Fiber Acidused in displacement step (#Zabove):

. 23.5 23 55 30 25.3 2; 60 30 1 2,500 Butync 1 Too much fiber.

Example V The preceding example was repeated except that the firstdisplacement of water used 250 parts of solvent as shown in thefollowing table. The results obtained with various solvents are asfollows, the figures given being the averages of dope from twoesterifications:

Tempierattire is- Ghmt y V smlgilicleiw (em') eoslty Colol I nei uid, C.

Solvent: Methanol. 30 20 20 70 15 Nitriles: Acetonitrilc 30 18 14 75 4OKetoncs:

Acetone 30 19. 5 22 70 220 Methyl ethyl kctonc 16 24 ('15 625 De ClarityVis- 1' grces (0111.) cosity 001m Esters:

Methyl formatc.. 20 18 12 75 35 Methyl acetate 30 15 27 70 50 Ethel-s:

Ethyl ether 20 12 S 75 300 Isopropyl ether 2O ll 75 7 50 Hydrocarbons:Benzene. 30 9 16 70 525 In each of the examples given above, thereaction masses can be precipitated by running this dilute acetic acidaccompanied by agitation and the precipitated cellulose esters can thenbe separated from the liquid in each case.

What we claim and desire to secure by Letters Patent of the UnitedStates is:

1. A process of activating cellulose for the formation of butyrylcontaining cellulose esters comprising subjecting the cellulose in sheetform to a water wetting, displacement of the water by a. displacementagent selected from the group consisting of methanol, ethanol, formicacid, acetic acid, acetone, acetonitrile, methyl ethyl ketone, andmethyl formate, and following this displacement with a seconddisplacement of the organic reagent with butyric acid.

2. A process of activating cellulose for the preparation of butyrylcontaining cellulose esters comprising subjecting the cellulose in sheetform to wetting with water, displacement of the water with methanol, andthen displacing the methanol with butyric acid.

3. A process of activating cellulose for the preparation of butyrylcontaining cellulose esters comprising subjecting the cellulose in sheetform to wetting with water, displacement of the water with acetonitrile,and then displacing the acetonitrile with butyric acid.

4. A process for preparing a cellulose acetate butyrate comprisingactivating cellulose in sheet form by a sequence consisting of waterwetting, displacement of the water with a displacement agent selectedfrom the group consisting of methanol, ethanol, formic acid, aceticacid, acetone, acetonitrile, methyl ethyl ketone, and methyl formate,and then a second displacement with butyric acid, and then esterifyingthe so treated cellulose with a butyrylation mixture comprising butyricanhydride and esterification catalyst.

5. A process of activating cellulose for the preparation of butyrylcontaining cellulose esters comprising subjecting the cellulose in sheetform to wetting with water, displacement of the water with acetic acid,and then displacing the acetic acid with butyric acid.

6. A process of activating cellulose for the preparation of butyrylcontaining cellulose esters comprising subjecting the cellulose in sheetform to wetting with water, displacement of the water with acetone, andthen displacing the acetone with butyric acid.

7. A process of activating cellulose for the preparation of butyrylcontaining cellulose esters comprising subjecting the cellulose in sheetform to wetting with water, displacement of the water with formic acid,and then displacing the formic acid with butyric acid.

GEORGE A. RICHTER. ERVIN L. PERKINS. LLOYD E. HERDLE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,752,596 Hubert et a1. Apr. 1,1930 2,315,973 Malm Apr. 6, 1943 2,478,396 Hincke et al Aug. 9, 19492,484,455 Herdle et a1 Oct. 11, 1949 2,487,892 Richter et al Nov. 15,1949 2,490,754 I-Iincke et al Dec. 6, 1949

1. A PROCESS OF ACTIVATING CELLULOSE FOR THE FORMATION OF BUTYRYLCONTAINING CELLULOSE ESTERS COMPRISING SUBJECTING THE CELLULOSE IN SHEETFORM TO A WATER WETTING, DISPLACEMENT OF THE WATER BY A DISPLACEMENTAGENT SELECTED FROM THE GROUP CONSISTING OF METHANOL, ETHANOL, FORMICACID, ACETIC ACID, ACETONE, ACETONITRILE, METHYL ETHYL KETONE, ANDMETHYL FORMATE, AND FOLLOWING THIS DISPLACEMENT WITH A SECONDDISPLACEMENT OF THE ORGANIC REAGENT WITH BUTYRIC ACID.